WARSAW (Reuters) - Donald Trump's election victory arose from voter discontent with ruling elites similar to that which brought Poland's conservative Law and Justice party (PiS) into power, Prime Minister Beata Szydlo said in an interview with Reuters.

Szydlo, in office since PiS won the 2015 parliamentary election, also said she was confident Trump would abide by NATO's commitment to bolstering its presence in eastern Europe in the face of Russia's renewed assertiveness in the region.

"Donald Trump ... reached the people in his campaign. He focused on their needs (and) positioned himself outside the political elite," Szydlo said in the interview, her first with a foreign news outlet since becoming prime minister.

"Something is changing in how politicians are being perceived and how people make their choices. People aren't picking politicians who are connected with the current political elites," the 53-year-old premier said.

"It's a clear signal ... that politicians are removed from reality. "People are saying, 'No, we don't want this'...This is how Law and Justice won in Poland."

The eurosceptic, nationalist-minded PiS unseated long-ruling centrists in last year's election on a promise of more economic fairness, national pride and Catholic values in public life.

It attracted a broad electorate disenchanted with its meager share of Poland's success in shedding communism and adopting a market economy over the past quarter century.

The PiS's popularity remains high thanks to higher welfare spending but its efforts to assert control of state institutions have deeply split Polish society and raised European Union fears about an erosion of Polish democracy and media freedoms.

Trump, for his part, rode a grassroots wave of anger toward Washington insiders to defeat Hillary Clinton, a former first lady, U.S. senator and secretary of state, at the election.

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Poland has viewed Washington as its most important ally since the 1989 collapse of its communist regime. But PiS drew unusually blunt criticism from U.S. President Barack Obama this year over its efforts to shackle Poland's constitutional court.

Speaking at a NATO summit in Warsaw in July, Obama called on the Warsaw government to do more to protect democracy.

Trump has said he will have a "very, very good" relationship with Russia and this could become a major concern for the PiS, which is deeply distrustful of Moscow.

Trump also unnerved European leaders with his suggestion that he could withdraw funding for the NATO alliance when asked during his election campaign whether the United States should protect allies that have low defense spending.

"Campaign dynamics are such that when it comes to government, the reality is slightly different, more coherent," Szydlo said about Trump's pre-election comments. "We need to wait calmly until the president-elect presents his program."

For Poland, the future of a decision at the NATO summit in Warsaw to deploy multinational forces in the three Baltic states and Poland to deter any possible aggression from neighboring Russia would be a particular concern.

"I am confident," Szydlo said when asked whether she was worried there was a risk the decision would not be implemented under the Trump administration, which takes office in January. "The decisions taken in Warsaw are crucial. They are important for peace in our region, for security, also globally," she said.

"We cannot take direction from the mood borne in an election campaign. Some decisions are taken regardless of changes in the administration in any country and they are later fulfilled."